Add StellaOps.Workflow engine: 14 libraries, WebService, 8 test projects

Extract product-agnostic workflow engine from Ablera.Serdica.Workflow into
standalone StellaOps.Workflow.* libraries targeting net10.0.

Libraries (14):
- Contracts, Abstractions (compiler, decompiler, expression runtime)
- Engine (execution, signaling, scheduling, projections, hosted services)
- ElkSharp (generic graph layout algorithm)
- Renderer.ElkSharp, Renderer.ElkJs, Renderer.Msagl, Renderer.Svg
- Signaling.Redis, Signaling.OracleAq
- DataStore.MongoDB, DataStore.PostgreSQL, DataStore.Oracle

WebService: ASP.NET Core Minimal API with 22 endpoints

Tests (8 projects, 109 tests pass):
- Engine.Tests (105 pass), WebService.Tests (4 E2E pass)
- Renderer.Tests, DataStore.MongoDB/Oracle/PostgreSQL.Tests
- Signaling.Redis.Tests, IntegrationTests.Shared

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/workflow/engine/13-backend-comparison-2026-03-17.json

@@ -0,0 +1,125 @@
+{
+  "date": "2026-03-17",
+  "type": "backend-comparison",
+  "status": "baseline-decision-pack",
+  "sources": {
+    "oracle": "10-oracle-performance-baseline-2026-03-17.json",
+    "postgres": "11-postgres-performance-baseline-2026-03-17.json",
+    "mongo": "12-mongo-performance-baseline-2026-03-17.json"
+  },
+  "validation": {
+    "integrationBuild": {
+      "warnings": 0,
+      "errors": 0
+    },
+    "oraclePerformanceSuite": "12/12",
+    "postgresPerformanceSuite": "11/11",
+    "mongoPerformanceSuite": "14/14",
+    "postgresBackendParitySuite": "9/9",
+    "mongoBackendParitySuite": "23/23"
+  },
+  "normalizedMetrics": {
+    "signalRoundTrip": {
+      "oracle": {
+        "serialLatencyAvgMs": 3104.85,
+        "serialLatencyP95Ms": 3165.04,
+        "throughputOpsPerSecond": 20.98,
+        "throughputAvgMs": 4142.13,
+        "throughputP95Ms": 4215.64,
+        "soakOpsPerSecond": 3.91,
+        "soakAvgMs": 4494.29,
+        "soakP95Ms": 5589.33
+      },
+      "postgres": {
+        "serialLatencyAvgMs": 3079.33,
+        "serialLatencyP95Ms": 3094.94,
+        "throughputOpsPerSecond": 25.74,
+        "throughputAvgMs": 3603.54,
+        "throughputP95Ms": 3635.59,
+        "soakOpsPerSecond": 4.30,
+        "soakAvgMs": 4164.52,
+        "soakP95Ms": 4208.42
+      },
+      "mongo": {
+        "serialLatencyAvgMs": 97.88,
+        "serialLatencyP95Ms": 149.20,
+        "throughputOpsPerSecond": 76.28,
+        "throughputAvgMs": 1110.94,
+        "throughputP95Ms": 1121.22,
+        "soakOpsPerSecond": 47.62,
+        "soakAvgMs": 322.40,
+        "soakP95Ms": 550.50
+      }
+    },
+    "capacity": {
+      "c1": {
+        "oracle": 3.37,
+        "postgres": 4.11,
+        "mongo": 7.08
+      },
+      "c4": {
+        "oracle": 15.22,
+        "postgres": 17.29,
+        "mongo": 38.35
+      },
+      "c8": {
+        "oracle": 21.34,
+        "postgres": 33.21,
+        "mongo": 66.04
+      },
+      "c16": {
+        "oracle": 34.03,
+        "postgres": 57.04,
+        "mongo": 68.65
+      }
+    },
+    "transport": {
+      "immediateBurstNightlyOpsPerSecond": {
+        "oracle": 50.18,
+        "postgres": 70.10,
+        "mongo": 46.18
+      },
+      "delayedBurstNightlyOpsPerSecond": {
+        "oracle": 10.71,
+        "postgres": 19.60,
+        "mongo": 16.66
+      }
+    },
+    "bulstrad": {
+      "quoteOrAplCancelSmokeOpsPerSecond": {
+        "oracle": 19.69,
+        "postgres": 59.88,
+        "mongo": 23.48
+      },
+      "quotationConfirmConvertToPolicyNightlyOpsPerSecond": {
+        "oracle": 1.77,
+        "postgres": 3.33,
+        "mongo": 10.83
+      }
+    }
+  },
+  "backendObservations": {
+    "oracle": {
+      "dominantWait": "log file sync",
+      "strength": "highest validation maturity",
+      "primaryPressure": "commit pressure"
+    },
+    "postgres": {
+      "dominantWait": "Client:ClientRead",
+      "strength": "best relational performance profile",
+      "primaryPressure": "queue claim and wake cadence"
+    },
+    "mongo": {
+      "dominantWait": "none-stable",
+      "strength": "fastest measured synthetic throughput",
+      "primaryPressure": "latency expansion from c8 to c16 and operational dependence on transactions plus change streams"
+    }
+  },
+  "recommendation": {
+    "currentPortabilityChoice": "PostgreSQL",
+    "reason": "best performance-to-operability compromise with a relational model and competitive backend-native validation",
+    "fastestMeasuredBackend": "MongoDB",
+    "highestValidationMaturity": "Oracle",
+    "caveat": "this is a baseline-level decision pack; Oracle still has the broadest hostile-condition and Bulstrad hardening surface"
+  }
+}